[openssl-users] EVP_EncryptUpdate and EVP_CIPHER callback do_cipher
beldmit at gmail.com
Mon Apr 18 15:04:35 UTC 2016
On Mon, Apr 18, 2016 at 6:00 PM, Matt Caswell <matt at openssl.org> wrote:
> On 18/04/16 15:55, Dmitry Belyavsky wrote:
> > Hello,
> > Could anybody explain how to deal with the output length in the
> > EVP_EncryptUpdate?
> > The function EVP_EncryptUpdate has the outl output parameter, which is
> > designed for returning the length of the resulting ciphertext. Then
> > internally it calls the do_cipher callback which does not take such a
> > parameter.
> > Is there a way to return an expected buffer length from the callback?
> > It may be necessary when we call the EVP_EncryptUpdate some times, and
> > we get the case when ctx->buf from the previous calls has enough bytes
> > to be processed together with the input buffer so the output is longer
> > then the input.
> The man page advises that the size of the output buffer should be:
> inl + cipher_block_size - 1
> This should cater for all eventualities.
SY, Dmitry Belyavsky
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